Organic shaped structures coated with werner-type chromium compounds and method of making the same



United States Patent O M ORGANIC SHAPED STRUCTURES COATED WITHWERNER-TYPE CHROMIUM COMPOUNDS AND METHOD OF MAKXNG THE SAME No Drawing.Application April 9, 1952, Serial No. 281,481

4 Claims. (Cl. 117139.5)

This invention relates to shaped structures having improved anti-staticproperties and to processes for producing the same. More particularly,it relates to films, filaments, fibers, monofils, coatings, fabrics andlike structures, having a moisture regain of no greater than fivepercent and a resistivity of at least 400,000X10 ohms, the surfaces ofwhich have uniformly distributed thereon as an anti-static agent acomplex compound of the Werner type in which trivalent nuclear chromiumatoms are coordinated with a monocarboxylic acid selected from the clasconsisting of p-nitrophenlacetic acid, p-nitrobenzoic acid, phenylaceticacid, trichloroacetic acid, thioglycollic acid, cyanoacetic acid andgluconic acid.

Films, filaments, fibers, monofils, coatings fabrics and like structureshaving low moisture regain and high resistivity have a propensity toready develop strong electrostatic charges which make them difficult tomanipulate during manufacture, subsequent processing and use, such as,for instance, in the steps of spinning, knitting, weaving, slitting,printing, perforating, winding, sealing, packaging and other finishingoperations. By reason of their highly charged surfaces, these articlesalso accumulate heavy dust deposits which, of course, are veryundesirable.

Then, too, in the manufacture of film for photographic uses having lowmoisture regain and high resistivity, the discharge of positive andnegative charges during processing exposes the light-sensitive silverhalides leaving characteristic static marks after development.

Various agents, methods and apparatus have heretofore been proposed toeliminate or at least minimize the accumulation of electrostatic chargeson shaped structures without detracting from their physical properties,but they are not entirely satisfactory.

Now I have found that the surface characteristics of films, filaments,fibers, monofils, sheets, coating and like structures having a moistureregain of no greater than 5% and a resistivity in ohms of at least400,000 1.0 can be improved by applying to the surfaces of thesestructures a Werner type chromium complex in which a trivalent chromiumatom is coordinated with a monocarboxylic acido group of the classconsisting of p-nitrophenylacetato, p-nitrobenzoato, phenylacetato,trichloroacetato, thioglycollato, cyanoacetato and gluconato; fromsolutions of such complexes, and thereafter drying said structures byany suitable expedient. These complex compounds are outstanding in thatthey Wet the surface of the shaped structure, resulting in asubstantially uniform, adherent coating application.

Chromium coordination complex compounds of the Werner type suitable foruse in accordance with my invention can be coordinated with any of theaforenamed monocarboxylic acids. A compound of the acid such as an esteror salt which can liberate the free acid under the condition of thecoordination reaction is, of course, equivalent to the free acid.

General methods for preparing suitable Werner type chromium acidcomplexes are described in ller Patents Nos. 2,273,040, 2,356,161 and2,524,803. The processes 2,745,770 Patented May 15, 1956 described in2,273,040 and 2,356,161 effect the reaction between a carboxylic acidogroup and a basic trivalent chromium salt of a monobasic acid in thesubstantial absence of free water. U. S. 2,524,803 teaches a methodwhereby contact between the basic chromium chloride and the carboxylicacido group .is effected in the presence of alcohol.

The nature of the Werner-type complex chromium compounds and thenomenclature applied to them is described fully in U. 5. Patents2,273,040, 2,356,161 and 2,524,803. By deleting the suffix -ic from thename of the carboxylic acid and adding the sufiix -ato a system ofnaming the acido groups coordinated with the chromium, and hence fornaming the chromium complexes, is provided. Thus, p-nitrophenylaceticacid gives p-nitrophenylacetato groups and the complex is calledp-nitrophenylacetato chromic chloride.

The Werner complexes are admixed with a suitable volatile solvent whichdoes not affect the complex, such as, for example, water, methanol,ethanol, isopropanol, t-butanol, aqueous solutions of these alcohols,and butyl acetate.

These solutions should contain from about 0.1% to about 1.0% by weightof the Werner type chromium complex.

Application of the solution of the Werner-type chromium complex to thesurface of the structure having a moisture regain of 5% or less andresistivity of at least 400,0O0X10 ohms can be accomplished by anyconvenient expedient which insures intimate contact of the complex withthe substrate. For instance, dipping, spraying, brushing, roll coating,paddling, and the like operations may be employed.

The temperature of the application bath is not critical but it should besuch that the chromium complex is dissolved or thoroughly dispersed. Ingeneral, the temperature should be maintained preferably below F.

Aqueous solutions of the Werner type chromium complexes are particularlywell suited for purposes of this invention. Should, however, the type offabric or fiber under treatment he very difficult to wet because of thepresence of sizing agents or other contaminates on the surface, it maybe necessary to add some isopropanol to the aqueous solution of thecomplex compound to improve the wetting characteristics, but in mostinstances this will not be necessary.

The shaped structure treated with an aqueous solution of a chromiumcomplex can be cured on a tenter frame, drum dryers or other suitableapparatus at a temperature of from to 250 F. for a period of from about1 to 5 minutes. Air drying will suffice.

The thickness of the anti-static layer is variable from that justsufiicient to form a uniform coherent coating to a maximum thicknessdetermined by the characteristics of the layer. Thus too thick a coatingmay lead to tackiness or flaking. While the optimum coating weight mayvary depending upon coating conditions, a practical range for film isfrom about 2 to 50 milligrams of complex per square yard of filmsurface. The preferred coating weight for photographic film is fromabout 0.15 mg. to 0.35 mg. total solids per square decimeter.

The shaped structures whose surfaces have uniformly distributed thereona Werner-type chromium complex may be in the form of films, filaments,fibers, monofils, coatings, fabric and the like but they are allcharacterized by having a moisture regain no greater than 5 per cent anda resistivity of at least 400,000X10 ohms.

By the term moisture regain is meant the per cent moisture in the shapedstructure based on a bone-dry basis. This definition is in accord withthat used in the art and is fully described by Bruce E. Hartsuch inhisthe circuit is measured with a microametcr.

" book lntroduction'to Textile Chemistry, John Wiley &

Sons, Inc., New York, 1950, at pages 118-122.

The American Society for Testing Materials has established a set ofstandard moisture regains, shown in Table 1 7- of the aforementionedHartsuch reference. The per cent moisture regain approximates the percent of water that each structure would absorb if exposed to an averageor normal atmosphere, which is assumed to have a relative humidity of65% at a temperature of 70 F. In other words, a percentage of moistureregain of 5 means that 5 per cent of water on a bone-dry basis isabsorbed by the shaped structure when exposed to an atmosphere having arelative humidity of 65% at a temperature of 70 F.

The term resistivity is used in its conventional sense to mean theelectrical resistivity of the shaped structures. The apparatus used todetermine the electrical resistance of the various structures is fullydescribed by Mason Hayek and F. C. Chromey in volume 40 of AmericanDyestufi Reporter, at pages 225-227.

The principle involved in the Hayek-Chromey instrument is themeasurement of the IR drop in a known resistance, where I is the currentleaking thru the sample. The voltage across the standard resistance isamplified with an electrometer tube, and the extent of the unbalance ofFrom a graph of the logarithm of the meter deflection against thelogarithm of the test resistance in standard resistor units, the unknownresistance can be determined.

Included among the shaped structures which have moisture regains of 5%or less and electrical resistivities of at least 400,000X ohms arepolyamides, polyesters, such as for instance polyethylene terephthalate,acrylic polymers, such as for instance polyacrylonitrile, vinyl polymersother than polyvinyl alcohol, vinylidene chloride polymers,vinyl-acrylic copolymers, polystyrene, polyethylene and the like.

The electrostatic voltages of the various shaped structures againstsynthetic rubber are measured by the method first described by D. I.Lehmicke, American Dyestuif Reporter 38, 853 (1949) and more recently byL. B. Chandler, Textile World 101, 116 (1951). In brief, the methodcomprises charging the shaped structure such as nylon fabric by rubbingit ten times with a neoprenegloved hand. The charged structure is thendropped into an aluminum beaker insulated from the ground and connectedto a voltmeter. The voltage generated is measured by reading thevoltmeter.

The nature of this invention and its method of application will bebetter understood by reference to the following illustrative examples:

Example 1 Example 2 A film strip composed of polyethylene terephthalateas described in Example 1 is coated on one side with an aqueous solutionheaving the following composition by weight:

7 Parts p-Nitrobenzoatolchromic chloride 0.156 Wetting agent (alkyl arylpolyether alcohol) 1.00 Water 4 100.00

The coating is dried at 160 F. for a period of three minutes. Thesurface resistivity of the treated film is 5000 10 ohms. The controluntreated film has a surface resistivity of l0,000,000 X 10 ohms.

Example 3 against synthetic rubber was determined by the aforementionedmethod of Lehmicke and Chandler. A voltmeter reading of 76 volts (78 F.,72% R. H.) was obtained for the treated fabric. The electrostaticvoltage of the nylon control (untreated) generated against syn theticrubber was 760 volts.

The treated nylon taffeta retained 6 mg./sq. ft. of the complex chromiumcompound.

Example 4 A 7 x 9 inch piece of polyethylene terephthalate tafletahaving a moisture regain of about 0.4% R. H.) and a resistivity ofgreater than 1,000,000 X 10 ohms was coated with. an aqueous solutioncontaining 0.6% by Weight of stock p-nitrophenylacetato chromicchloride.

The treated fabric was dried and its electrostatic voltage generatedagainst synthetic rubber was then determined. The treated fabricgenerated 140 volts against neoprene while the polyethyleneterephthalate control fabric generated 960 volts.

. The polyester taffeta treated with the p-nitrophenylacetato chromicchloride retained about 4 ing/sq. ft. of the chromium complex.

I claim:

1. A method which comprises applying to an organic shaped structurehaving a moisture regain of no greater than 5% and a surface resistivityof at least 400,000 X 10 ohms a solution containing a complex chromiumcompound of the Werner type selected from the group consisting ofp-nitrophenylacetato chromic chloride, p-nitrobenzoato chromic chloride,phenylacetato chromic chloride, trichloroacetato chromic chloride,thioglycollato chromic chloride, cyanoacetato chromic chloride andgluconato chromic chloride, and subsequently drying said 2. A methodwhich comprises coating an aqueous solution of a complex compound of theWerner type in which a trivalent nuclear chromium atom is coordinatedwith a monocarboxylic acido group of the class consisting ofp-nitrophenylacetato, p-nitrobenzoato, phenylacetato,trichloroacetato,.thioglycollato, cyanoacetato and gluconato groups ontoa surface of an organic shaped structure having a moisture regain of nogreater than 5% and a surface resistivity of at least 400,000 X10 omhsand subsequentlydrying said coated structure.

3. A method which comprises coating a solution containing a volatilesolvent and a complex compound of the Werner type said complex chromiumcompound being selected from the group consisting ofp-nitrophenylacetato chromic chloride, p-nitrobenzoato chromic chloride,phenylacetato chromic chloride, trichloroacetato chromic chloride,thioglycollato chromic chloride, cyanoacetato chromic chloride, andgluconato chromic chloride, in which a trivalent nuclear chromium atomis coordinated with a monocarboxylic acido group of the class consistingof pface resistivity of at least 400,000 X 10 ohms and dry- ReferencesCited in the file of this patent ing the layer- UNITED STATES PATENTS 4.Organic shaped stmctures the surfaces of which have uniformlydistributed thereon as an anti-static agent a Her 1 1942 complex hromiumcompound of the Werner-type, said 5 2,356,161 r Aug. 22, 194 pl xhromium compound being selected from the 2,532,691 e y Dec.5,1950 groupconsisting of p-nitrophenylacetato chromic hlo- 2,628,176 Simon et a11953 ride, p-nitrobenzoato chromic chloride, phenylacetato 2,647,336 'f4, 1953 chromic chloride, trichloroacetato chromic chloride, thio- 102,673,824 mefeld et a1 1954 glycollato chromic chloride, cyanoacetatochromic chlo- 2673825 Blefeld et a1 1954 ride, and gluconato chromicchloride, said structures hav- OTHER REFERENCES mg Prior to surfaceapplication of Said chromium Knowlton: Standard Handbook for ElectricalEngipound a moisture regain no greater than 5% and a surface nears 7thedition 1941 4 595 e resistivity of at least 400,000 X 10 ohms. 15 S Pag

1. A METHOD WHICH COMPRISES APPLYING TO AN ORGANIC SHAPED STRUCTUREHAVING A MOISTURE REGAIN OF NO GREATER THAN 5% AND A SURFACE RESISTIVITYOF AT LEAST 400,000 X 10**8 OHMS A SOLUTION CONTAINING A COMPLEXCHROMIUM COMPOUND OF THE WERNER TYPE SELECTED FROM THE GROUP CONSISTINGOF P-NITROPHENYLACETATO CHROMIC CHLORIDE, P-NITRO BENZOATO CHROMICCHLORIDE, PHENYLACETATO CHROMIC CHLORIDE, TRICHLOROACETATO CHROMICCHLORIDE, THIOGLYCOLLATO CHROMIC CHLORIDE, CYANOACETATO CHROMIC CHLORIDEAND GLUCONATO CHROMIC CHLORIDE, AND SUBSEQUENTLY DRYING SAID STRUCTURE.